Modelling Glaciers in the ALADIN-HIRLAM Numerical Weather Prediction SystemEmily Gleeson*1

,Ruth Mottram2, Kristian Pagh Nielsen2, Xiaohua Yang2

1 Met Éireann, Dublin, Ireland2 Danish Meteorological Institute, Lyngbyvej 100, Copenhagen, Denmark

Model Evaluation: snow cover and albedo

AbstractHARMONIE (a canonical configuration of ALADIN-HIRLAM) is a convection permitting non-hydrostatic model that includes the multi-purpose SURFEX surface model. It is developed for highresolution (1-3 km) weather forecasting and used for a number of different regions in Europe andthe Mediterranean. The version HCLIM is being developed for regional climate modelling. Here werun it for Greenland. By improving the characterisation of glacier surfaces within SURFEX we showthat weather forecast errors over both the Greenland ice sheet and smaller glaciers can besignificantly reduced. The improvements also facilitate increasingly accurate ice melt and runoffcomputations, which are important both for ice surface mass balance estimations and forcommercial applications such as hydropower forecasting. These improvements will also benefitforecasting for HARMONIE domains that cover the Svalbard archipelago, the Alps and theScandinavian mountain glaciers. Future uses of HCLIM for these regions, where accuratelycharacterising glacial terrain will be crucial for climate and glaciological applications, are alsoexpected to benefit from this improvement.

Figure 1. Harmonie NWP (numerical weather prediction) domains forGreenland and Iceland: a) is GLB NWP domain for Greenland (also used indevelopment here) b) IGA domain over which model updates will beapplied when complete c) PROMICE automatic weather stations aroundGreenland, QAS_L station is used for model testing.

Scan QR codeto go to polarportal.org

HARMONIE Set-UpHARMONIE has many different set-up possibilitiesand can be run with different physical, dynamical andsurface schemes. Here we use the DMI GLBoperational NWP set-up shown in Figure 2.

Future WorkThis preliminary work is encouraging; we expect to have a working glacier scheme in HARMONIE this year but the following are still missing:• Surface albedo of bare ice, Surface Mass Balance

computation; Retention and Refreezing in the snowpack (CROCUS in SURFEX is one solution).

Figure 3. Operational (GLB) HARMONIE represents weather over the ice sheet well as shown here -clockwise from top left: 2m temperature, wind speed, cloud cover (note observations are uncertain below 0.2) and relative humidity when compared with QAS_L data, upper 4 plots March, lower 4 plots July 2014.

Figure 4 compares skin temperature at QAS_L to output from HARMONIE for the default and modified cases.

Figure 6. (left) Comparison of observed andmodelled skin temperature compared with measuredsnow height at QAS_L (right) the albedo in differentshortwave bands over same period.

Figure 7. (upper left) Total albedo with cloud cover masked out for one day in July, (upper right) over glaciers (lower) MODIS (MOD10A) average over 1 week. HARMONIE total albedo is too low over bare ice

SURFEX: Land surface

AladinDynamics

ECMWF IFS cycle 41r1D95 snow

scheme

IFS Radiation

QAS_L

ab c

Figure 8. Latent (LHF) and Sensible (SHF) heat fluxesfor two days in July 2015, the 7th was a high melt day,the 27th was a relatively low melt day compared withthe Greenland melt extent courtesy of Peter Langen,DMI calculated from the HIRLAM-newsnow modelavailable on polarportal.dk.

LHF is much higher than the SHF on both days (notedifferent colour scale) and the pattern correlates wellwith melt extent from HIRLAM. Fausto et al. (2016)have recently questioned model simulations of thedifferent types of heat fluxes during extreme meltevents. Further work on this is needed for which bothHCLIM and HARMONIE will be useful.

Non-radiative fluxes

LHF SHF

Melt extent

MESO-NH: Physics

When snow melts away from the glacier surface andbare ice is exposed, modelling results deteriorate,suggesting an inadequate surface parameterisation.

We modified HARMONIE to simulate melting over iceby fixing the radiative surface temperature. ModifiedHARMONIE simulates the melt out of surface snowreasonably well but there is a cold bias in the skintemperature as shown in Figure 4 below.

Figure 5. Change in Snow Water Equivalent (kg m-2) from (left) 1st April to (right) 31st August 2015.

LHF SHF

Melt extent

7th July 2015

27th July 2015